The jam-band faithful came from Denver and Boulder and points east and west; they trudged and they danced in deep, slushy snow as they descended upon Buttermilk for The Après. Aspen Skiing Co.’s new music festival ran Friday through Sunday with destination performances by headliners The String Cheese Incident and Umphrey’s McGee.

Playing in typically temperamental spring weather — ranging from T-shirt warm afternoons to parka-cold nights with a few squalls of rain, sleet and snow — the bands drew attentive and jubilant crowds to the mountainside from its fervent local, regional and national fan bases, including many who’d seen them dozens of times and regularly travel for performances.

Bill Finn of Denver said he’d seen 140 Umphrey’s shows before this weekend and about 90 by String Cheese. He came to the festival with a group of childhood friends from Chicago who’ve since spread across Colorado and California and who regularly travel for Umphrey’s tours. Among them was Amanda Eilers of Santa Cruz, California, who said seeing the bands in this unique mountain venue made The Après a must.

“It’s cool to see them in a spot like this,” she said. “I feel like they let loose and they know it’s special.”

Others from the local contingent of hardcore fans said the affordability of The Après was a relief.

“This was priced for the locals and that feels good,” said Kat Mahoney of Snowmass Village, attending her 52nd Umphrey’s show Friday.

A $200 three-day ticket to the festival included two days of skiing Aspen’s mountains, which also was a draw for the regional segment of the crowd.

“It was a good deal,” said Ryan Howell of Colorado Springs, who road-tripped with a group of friends and made his first trip to Aspen for The Après. “It enticed us to drive five-and-a-half hours.”

Members of both bands also skied in the week leading up to the shows and took the stage in high spirits.

“This is f-ing crazy to be playing on a mountain right now,” Umphrey’s lead singer and guitarist Brendan Bayliss told the crowd on Friday.

In the final show of its spring tour, Umphrey’s McGee played a typically diverse two-hour set that wavered from psych rock to speed metal and noodling guitar jams, along with a dueling banjo-styled back-and-forth between Bayliss and guitarist Jake Cinninger on the tail end of “Higgins.”

The performance included an extended take on “Bad Friday” that transitioned into a cover of The Police’s “When the World is Running Down, You Make the Best of What’s Around” and closed with the fan favorite “Hurt Bird Bath.”

On Saturday, String Cheese Incident hooked the crowd at the outset, playing “Texas,” a folksy road-trip tale from its first album that elicited a roar to the lyric “It was springtime in the mountains.” True to form, String Cheese hopped between sit-down acoustic songs and improvisational electric passages, interspersed with a few EDM freak-out jams and an extended take on “One Step Closer.” Playing two sets across about three hours, the band reached back to its earliest songs and showcased some of its newest — including the immigration-themed “Illegal” and the Beats Antique collaboration “Bhangra Saanj,” both released this winter — and sing-along favorites like “Barstool.”

“This is where we cut our teeth, playing ski areas and whatnot,” String Cheese’s Bill Nershi told the crowd, recalling their earliest days as an après-ski act in Crested Butte. “It’s good to be at the base of a mountain again.”

Held in a temporary open-air amphitheater on Panda Peak, the venue setup was similar to the X Games concerts there for the past four years. The crowds’ sizes appeared comparable to the X Games concerts — which have tallied as many as 5,000 on the snowy bunny hill — except that it was filled with crunchier devotees of guitar-based music rather than the heavily caffeinated teens who throng the mountain for X Games’ hip-hop and EDM stars.

The snowy terrain was difficult to navigate on foot. Soft and slushy snow that made for ideal spring skiing conditions over the weekend also made it challenging for concert-goers to keep their footing while navigating the sloped venue of The Après.

While most came with sturdy snowboots — and, of course, some wore ski and snowboard boots — many in the crowd came wearing slip-ons and sneakers (and at least one concert-goer came sockless in Birkenstocks).

This festive crowd did come prepared with costumes. Among the full-body furry suits on display included an avocado, a dinosaur and a chicken.

A man who identified himself as “Front Range Beaver” was decked out in a full beaver suit with a “Happy Birthday” balloon floating up from the tail (he and a group of Denver area friends with Ikon ski passes came to The Après to celebrate his 31st birthday).

While the crowds poured in for the headliners, the opening bands played to scant listeners — most notably during Southern Avenue’s 4:30 p.m. performance on Saturday, which had little more than two dozen people lining the stage at the outset.

The festival was co-promoted by Belly Up Aspen, the downtown music club that hosted more intimate performances by Umphrey’s on Wednesday and Thursday and one by String Cheese on Friday. The Buttermilk crowd was abuzz Friday with news that Jason Hann, percussionist for String Cheese, sat in with Umphrey’s at Belly Up on Thursday.

Skico has not committed to making The Après an annual event. The festival was announced in late January and successfully boosted tourist bookings during a lull between spring break and Easter weekend. Festival producer Deric Gunshor, Skico’s event development director, said Thursday that the future of The Après would depend upon how this year’s offering went, on the holiday calendar and booking trends of future ski seasons and, most importantly, on the ability to book “the right bands.”

Landing Umphrey’s and String Cheese — two of the most popular bands in ski country, with long-forged local ties and a fervent national following that travels to see them — was a coup for Skico.

“Attendance is driven by fans of the bands,” Gunshor said. “We can create an atmosphere around a spring event but people are going to turn out for a band that they are fans of.”